Fuse plug



Feb. 21, 1950 G. E. HOLMES 2,498,124 FUSE PLUG Fiied July 20, 1945 ATTD RN EYE Patented Feb. 21, 1950 OFFICE oss PLUG;-

Application luly' 20; 1945; Serial; 606*,113; 1

1 10 Claims.

The present invention relates to fuse plugs of the type whichrcontain a plurality of fuse elements andwhich permit a new'element to be brought into service when the element formerly in-service is blown.

A fuse plug of this type-is' shown in my Patent No. 2,383,484 of August 28, 1945. The construction shown in this-patent-is extremely simple and economical to manufacture. In order to bringa new fuse element into service, however. itis necessary to unscrew the-fuse and-remove it from the socket and then to withdraw the fuse carrier partially from the assembly before it can be turned to establish connection with a ne-wfuse element; The present invention overcomes: this inconvenience while retaining the simplicity of construction of'the fuse plug shown in the earlier patent.

An object of the invention is to provideafuse plug of thischaracter in which a new fuse elementisbrought into service-by rotation of -the threadedshell; A threaded shell is -anecessary Part of any fuse plugandbymaking-it rotatable and providing it with a contact member to engagethe various fuse links, thesame part is made to serve a double purpose thereby increasingthe economy of manufacture.

Other and further objects will=become apparent upon reading the following spec-ification together with the accompanyin drawin forming a part hereof.

Referring tothe drawing:

Fig. 1 is a sectional view in elevation,

Fig. 2 is a sectional plan view along the line 2'2of Fig.

Fig. 3 is a sectional plan view taken along the line 3-3 of Fig. 1,

Fig. 4 is a vertical section of the head portion,

Fig. 5 is a side view of the fuse carrier;

Fig. 6 is a sideview of the fuse element unit,-

Fig; 7 is a plan view of an arc barrier ring,

Fig. 8" is afragmentary plan view of a modification of the invention and'except for the modification is otherwisethesame as Fig. 3;

Referringto Fig; l, a hollow head 2 which serves'to grip the device; when inserting it in a fuse socket or; unscrewing it; therefrom is shownprovided with a l rality of longitudinalinternal ribs 3 which engage corresponding grooves; I!

infuse carrier-l. The head; 2 andv fusecarrier. 1

thus rotate, together as a unit-i liead-tandfuse carrier. 1 are both COnStIiu CtEdlOfffS'Llit&b16fdielectric material andhead 2* maybe ofg lass; pen. mitting observation asto whichofthefuse. elements have been blown. Head" 2* and fuse carrier I maybe held together by suitable adhesive materialenga-ging ribs 3 or'in. any other desired manner.

An integrally formed fuse member comprising a piece of-fusemetal HIv is shown with downwardly and radially extending legs l2, each leg constituting an individual fuse element and being necked at l3 in'theusual manner to localize the point of arcing when the fuse element is blown. The width of the necked portion also serves to determinethe rating of the fuse. The fuse elements fit into corresponding upwardly sloping grooves l5 in fuse carrier l which provide an individual arcing chamber for each fuse element.

Commoncontact to the several fuse elements is established through a pin In which engages fusemember 14, the pin it being headed at H. Thelower head at the central bottom projection lfl of fusecarrier 1 is disposed to engage a contact in a fuse socket in the usual manner.

Threaded contact shell 6- is freely rotatably mounted on the assembly consisting of" fuse carrier T- and head 2'. The upper inwardly turned lip-5.of=shell 6- engages annulargroove 4 in head 2; The lower portion is provided with an inwardly extending flange 6a which engages the upper-surface of baseportion 8 of fuse carrier 1 applying suitable contact pressure at the lower head of pin IO- when the entire assembly is screwedintoa fuse socket. The gap between the lower portion'ofhead 2 and the lower flange 8a of shell Bisfilled by a partial rin of suitable insulating material adapted to prevent the arc accompanyin the blowing of the fuse element in service fromdamaging a fuse element in an adjacent groove.

Aninwardly extending spring contact member l-8-is permanently connectedto the lower in-- ternal' portion of shell 6 both electrically and mechanically and engages the lower portion of the particular fuse element I2 which is in service. The other elements are insulated by the lower wall; of head 2 and by barrierring l9. Spring l8. is shaped to act in a manner similar to thatof' a ratchet. Shell 6 may be rotated in onev direction to bring successive fuse elements into service. When moved in this direction it willmove outwardly over one of theribs l6 and s;pri1'l g-ybaclr to engage the fuse element in the next groove. This action serves as a detent mechanism so that engagement with the next fuse element: may be determined both by feel and. heaudi le. click s c a sp ing l8 snaps. ack; t ts. orma sit o fte passing the rib l6; Rotation in the opposite direction relative to head 2 and fuse carrier 1 is prevented by the contact spring l8 which will engage the side of one of the grooves l5.

Contact spring [8 may take the form shown in Fig. 3 or it may take the modified form shown at l8 in Fig. 8. It may also take any other desired form embodying the same principle of operation. The switching action to bring a new fuse element into service may take place either on rotation to'screw the fuse plug into the socket or on rotation in a direction to unscrew the plug. The shell 6 may be provided with either a right hand or a left hand thread. The embodiment illustrated shows a right hand thread with a new fuse element being brought into service upon turning the head in a direction to screw the plug into a fuse socket. The modification required to obtain any other desired combination will be ohvious to those skilled in the art.

Ordinarily, it will be desirable to have a new fuse element brought into service upon turning head 2 to screw the fuse plug into the socket. This insures that the fuse plug may always be unscrewed even if it is held by considerable friction. The assembly comprising the glass head portion 3 and the fuse carrying inner core portion in the form illustrated are secured together for common rotation by the interfitting tongue and groove arrangement best shown in Fig. 2. The threaded contact shell 6 howeveris freely rotatable relatively to this assembly, except for the spring pressed frictional engagement provided by the spring pressed contact pawl IS in one rotative direction, and in the opposite rotative direction, by the ratchet locking action of the pawl.

For example, Fig. 3 shows the pawl l8 arranged for a contact shell 6 having right hand screw threads, which is standard practice at present at least in the United States. In this case the turning moments for screwing the device into and out of a fuse socket will be applied to the head-core assembly by grasping and turning the annular top flange of the head 2. The spring frictional grip of the pawl [8 with the fuse carrying core, is sufficient to cause the shell to rotate with the head-core assembly for screwing the entire fuse plug into a usual fuse socket until the bottom of the central contact ill engages the usual central contact member in the fuse socket, not shown. The screwing of the fuse plug into its socket is permitted in a usual manner since the threaded shell 6, like all threaded fuses of this general class, are made to fit freely in their fuse sockets.

Once the central fuse plug contact member ID bottoms in the fuse socket, it causes a slight frictional jamming action between the threads of the contact shell 6 and the usual threaded wall of the socket sufficient to arrest further rotation of the shell. After this occurs, further rotation of the head-core assembly in a direction to screw the fuse plug into its socket will cause the headcore assembly to rotate relatively to the thus stationarily held threaded contact shell 6. This relative rotation causes the spring pressed contact pawl I8 to cam over the raised intervening barriers l6 between the grooves for adjacent fuse strips l2. As the spring pressed pawl passes each successive barrier it snaps inwardly into the next succeeding fuse groove in the core 1, contacting the fuse strip therein. These snappings of the spring pressed contact pawl are audible and also can be clearly felt by the one turningthe fuse. When a fresh fuse .plug is first inserted me,

socket with all of its fuse elements intact, it is immaterial on which fuse strip or leg I2 the contact pawl rests. The narrow necked blowout portions l3 of the fuses are visible through the glass of the sides of the head portion 2, and it is thus possible visibly to check the condition of the fuse elements.

When a fuse strip or leg [2 blows, as its destruction by an excess current load is termed, the line 'whichthe' fuse protects should be cleared of the condition which caused the fuse to blow. The head-core assembly then may be rotated in the direction tending to screw the contact shell 8 into its socket, until the first click of the pawl spring is heard and felt by the one doing the turning." When this occurs the next successive fuse strip or leg is contacted by the pawl and the fuse is ready for re-use. When all of the fuse strips or legs l2 have been blown, the entire fuse plug may be removed' from its socket by a counter-rotation or unscrewing of the core-plug assembly.

As clearly shown in Figs. 3 and 8 this counterrotational or unscrewing torque moment causes the pawl l8 or l8 to lock against the radially disposed wall of the groove in which the pawl is resting. This locking action of the pawl is sufficient to overcome the frictional or slight jamming action which held the threaded shell 5 against rotation during the rotation of the head-core assembly for changing fuse strips l2 as above set forth.

All unblown fuse strips or legs may be seen through the sides of the glass head 2. The blowing of one fuse strip or leg 12 will blacken up its own window section which the glass overlying its enclosing channel aptly may be termed. The blowing action of one fuse strip however is not permitted to spread laterally to other channels or fuse strips, since each channel for a fuse strip is sealed laterally from adjacent channels by the interfitting-of the abutments I5 on the plug against the ribbed inner face of the head as best shown in Fig. 2.

The channels for the fuses open into the space between the top of the fuse plug 1 and the head 2 to permit expansion of the small amount of gas created by the blowing of the fuse. It is obvious from the above description and the accompanying drawings that the interior is not hermetically sealed so that no dangerous pressures can build up in the interior of the glass head 2.

- -While the fuse carrying plug 1 may be adhesively secured in inserted position in the glass head 2, it will work satisfactorily if merely inserted therein, so as to have frictional engagement therewith. In such arrangement, even though the plug should be inserted loosely in the head, when the entire fuse plug is screwed into a socket, the contact member Iii, engaging the bottom of the socket as described previously herein, will force the plug up into properly seated position in the head and squeeze the parts into sealing relation with the insulating washer [9. With the head and fuse carrying plug thus assembled, the fuse carrying plug 7 can be replaced by a new one using the same head for still further economy of operation if desired.

I have shown what I believe to be the best embodiment of my invention. I do not wish, however, to be limited to the embodiment shown but what .I desire to secure by Letters Patent is set forth in the appended claims.

p d rela se reta i s carrier having a plurality of upwardly and inwardly extending grooves therein, a head member secured to the carrier by engagement with flanges intermediate the grooves and partially enclosing the carrier, a fuse member having plurality of outwardly and downwardly extending legs each leg forming a fuse element disposed within one of the grooves, a central connection from the fuse member to the lowermost portion of the carrier, a threaded contact shell freely rotatably secured to the head member and having an inwardly extending flange portion adapted to exert downward pressure on the carrier when the device is tightened into a fuse socket, and a spring contact member carried by the shell and disposed to establish successively an electrical connection to each of the fuse elements upon rotation of the shell with respect to the carrier.

2. A device as in claim 1 in which a circular member of insulating material is disposed within the shell rotatably therewith intermediate the lowermost portion of the head member and the upper surface of the flange portion of the shell and is provided with an opening permitting the spring contact member to pass therethrough to establish contact with the fuse elements.

3. A device as in claim 1 in which the contact member carried by the shell successively establishes connection to the fuse elements upon rotation in one direction and prevents rotation of the shell with respect to the carrier in the opposite direction.

4. A device as in claim 1 in which the contact member carried by the shell is secured directly thereto.

5. A device as in claim 1 in which the contact member carried by the shell is secured directly thereto and is further arranged to establish connection successively to the fuse elements upon rotation in one direction and to prevent rotation of the shell with respect to the carrier in the opposite direction.

6. In a device of the class described, a fuse carrier having a plurality of grooves therein arranged around a central rotative axis, a head member having interfitting relation with the fuse carrier, and secured to rotate with said fuse carrier, the portions intermediate the grooves comprising barriers, fuse strips in said grooves, a central electrically conductive connection from the fuse strips to the lowermost portion of the fuse carrier, a threaded contact shell freely rotatably secured to said head and fuse carrier, a portion of said shell being adapted to exert downward pressure on the central connection when the device is screwed into a fuse socket, and a spring pressed contact member carried by the shell and disposed to establish successively an electrical connection to each of the fuse elements on rotation of the head and carrier relatively to the shell.

7. A device as in claim 6 wherein the barriers intermediate the grooves are in sealing contact with the head member.

8. A device as in claim 6 wherein the barriers intermediate the grooves have interfitting relation with correspondingly shaped portions of the head member.

9. A device as in claim 6 wherein the spring contact member comprises an arcuately shaped strip of electrically conductive spring metal shaped to fit conformingly within the contact shell to rotate therewith, and having an inwardly offset pawl end portion disposed to contact successive fuse strips upon rotation of the shell relatively to the fuse carrier in one direction and. to prevent rotation of the shell relatively to the fuse carrier in the opposite direction.

10. A device as in claim 6 wherein the spring contact member comprises a pawl having frictional engagement with the secured head and fuse carrier upon rotation of the contact shell in one direction relatively thereto, and having interlocking engagement with said secured head and fuse carrier to prevent relative rotation of the contact shell in the opposite direction.

GEORGE E. HOLMES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,437,905 Moss et al. Dec. 5, 1922 1,437,906 Moss et al Dec. 5, 1922 1,848,924 Ammerman Mar. 8, 1932 1,914,871 Siampos June 20, 1933 2,058,264 Schiller Oct. 20, 1936 2,206,785 Linton July 2, 1940 2,383,484 Holmes Aug. 28, 1945 

